Salmeterol, 4-hydroxy-.alpha..sup.1 -6-(4-phenylbutoxy) hexyl!amino!methyl-1,3-benzenedimethanol, is a drug belonging to the general class of beta-adrenergic compounds. The prime action of beta-adrenergic drugs is to stimulate adenyl cyclase, the enzyme which catalyzes the formation of cyclic-3',5'-adenosine monophosphate (AMP) from adenosine tri-phosphate (ATP). The cyclic AMP formed mediates the cellular responses. Salmeterol acts selectively on beta.sub.2 -adrenergic receptors to relax smooth muscle tissue, for example, in the bronchial system. Salmeterol is most commonly used to treat bronchial spasms associated with asthma. Its activity is similar to that of albuterol which is the active component in well-known commercial bronchodilators such as Proventil and Ventolin. However, the beneficial effects of salmeterol are longer lasting than those of albuterol. Thus, use of salmeterol is more desirable than use of albuterol.
The form in which salmeterol is presently used is a racemic mixture. That is, it is a mixture of optical isomers, called enantiomers. Enantiomers are structurally identical compounds which differ only in that one isomer is a mirror image of the other and the mirror images cannot be superimposed. This phenomenon is known as chirality. Most biological molecules exist as enantiomers and exhibit chirality. Although structurally identical, enantiomers can have profoundly different effects in biological systems: one enantiomer may have a specific biological activity while the other enantiomer has no biological activity or may have an entirely different form of biological activity.